Compressor blade root seal

ABSTRACT

A sealing device for restricting leakage across the stages of an axial compressor through the clearances around the root fittings of replaceable blades. A compliant dished annulus is attached on the high pressure side of each compressor stage at its inside radius. The combination of centrifugal force and pressure differential across each compressor stage deforms the sealing device against the blade root fittings thereby restricting the leakage.

United States Patent Memery 154] COMPRESSOR BLADE ROOT SEAL [72]Inventor: James P. Memery, Manchester,

Conn.

[73] Assignee: The United States of America as represented by theSecretary of the Navy 22 Filed: May3, 1971 21 App].No.: 139,642

[52] 0.8. CI ..4l6/219, 416/221 [51] Int. Cl ..F01d 5/32 [58] Field ofSearch ..4l6/2l9, 500, 220, 230,221

[56] References Cited UNITED STATES PATENTS 2,998,959 9/ 1961 Haworth eta1. ..4l6/22l 3,070,351 12/1962 Hunt ..4l6/221 Oct. 24, 1972 3,266,7708/ 1966 Harlow ..4 1 6/220 3,295,825 1/1967 Hall ..416/221 FOREIGNPATENTS OR APPLICATIONS 1,138,797 2/1957 France ..416/500 PrimaryExaminer-Everette A. Powell, Jr. AttorneyR. S. Sciascia and Henry Hansen[57] ABSTRACT A sealing device for restricting leakage across the stagesof an axial compressor through the clearances around the root fittingsof replaceable blades. A compliant dished annulus is attached on thehigh pressure side of each compressor stage at its inside radius. Thecombination of centrifugal force and pressure dif ferential across eachcompressor stage deforms the sealing device against the blade :rootfittings thereby restricting the leakage.

6 Claims, 3 Drawing Figures PATENTEBum24 I972 3. 700.354

INVENTOR.

JAM ES P. MEMERY Hu Um ATTORNEY COMPRESSOR BLfAlpE RoorsEAr; STATEMENTor GOVERNMENT INTEREST The invention described herein .may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION The present invention relates toimprovements in axial compressors, and more particularly to a sealingdevice for restricting blade root fitting leakage in compressor rotorstages having removable blades.

Axial gas turbine compressor rotors commonly use dovetail broached slotsfor the attachment of the blades to the rotor disk. This attachmenttechnique is used for the purpose of facilitating blade replacement.Consequently in order to accommodate the normal manufacturing tolerancesof the blade root fitting a clearance is necessary in each slot. Theresult is that some of the compressed gas behind each compressor stageleaks back through these clearances into the preceding stage reducingsubstantially the overall efficiency of the gas turbine power plant. Inparticular where the pressure increment across the stage is large theleakage rate becomes significant, thus degradation of compressorefficiency is not minimized by staging optimization.

Various techniques of providing blade root sealing have been developedwithin the prior art to limit this leakage. Most of these techniquesprovide individual sealing devices attached at each blade root, therebymultiplying the number of components in a compressor with the attendantproblems of reliability and weight.

SUMMARY OF THE INVENTION Accordingly, it is the general purpose andobject of the present invention to provide a blade root seal integrallyformed as one unit. Other objects are to providea blade root seal thatis durable, replaceable and minimally affecting the existing compressordisc parameters.

These and other objects are accomplished according to the presentinvention by providing an annular seal generally dished to conform withthe convolutions of the blade attachment rim of the compressor discattached on the high pressure side thereof. The seal is formed from acompliant material such as metal foil and is pressed into sealingcontact by the combination of the pressure differential across the stageand the centrifugal force.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall side view of anaxial compressor shown partly in cross section illustrating a threestage compressor;

FIG. 2 is a plan view of a fragment of a compressor disc assembly asviewed from the high pressure side along section 2-2 of FIG. 1; and

FIG. 3 is an enlarged fragmentary view in cross section of thecompressor disc assembly taken along section 2--2 of FIG. 1.

" H'IDESCRIPTION OF THE PREFERRED EMBODIMENT I As shown in FIG. 1 anaxial compressor section 25 of a gas turbine is contained within thecompressor housing 26. A rotor unit consisting of three compressor discassemblies 10 mounted on a rotor shaft is enclosed by the housing 26having stator rings 27 mounted to the housing 26 interspaced betweenadjacent assemblies 10. Each compressor disc assembly 10 includes blades16 peripherally mounted on a disc 15 having an annular seal 11 coveringthe high pressure side of the blade mounting interface according to thepresent invention.

As shown in more detail in FIG. 2 each compressor disc assembly 10includes a plurality of removable blades 16 radially extending frommounting slots 12 formed in a peripheral flange 14 of a disc 15. Eachblade 16 includes a root end fitting 17 formed to engage in lockingarrangement the convolutions of the slot 12. A locking device 19commonly engages each blade 16 to disc 15. Each blade root fitting 17 isshown in partial contact with the convolutions of the slot 12 generallyin the areas of radial stress force transfer path being placed inabutment therewith either by the centrifugal force generated by therotation of disc 15 or by the locking mechanism 19. Thus the blade 16 islocated in the slot 12 in a manner that produces the highest leakagerates if clearances exist between the convolutions of the slot 12 andthe blade root fitting 17. As illustrated each blade root end fitting 17is dimensionally limited to allow for clearances 18 as is necessary toaccommodate various manufacturing tolerances. The total area ofclearances 18, which typically accumulates to an order of magnitude ofapproximately I to 2 square inches in a medium sized jet power plant, isa primary source of unwanted pressure leakage across the compressordisc. To limit this leakage a thin foil annular seal 11 is installedaccording to the present invention extending outwardly from rim 14.

Referring to FIG. 3 the peripheral rim 14 of disc 15 typically increasesin cross section with increasing radius in order to most effectivelytransmit the bearing forces generated by the angular motion of theblades 16 within corresponding slots 12. Accordingly, the seal 11 placedacross the slots 12 will be pressed against the blade roots 17 bycentrifugal force C.F. Seal 11 is formed out of thin metal sheet stockof a thickness sufficient to straddle the clearances 18, attached bydiffusion bonding at the inside radius thereof to the inside radius ofthe peripheral flange of disc 15, being preformed in the shape of aconcave annulus to generally mate with the convolutions of the flangeand is placed in sealing contact therewith by the centrifugal force CF.and pressure differential AP. The outer radius of seal 11 is formed toprovide a sealing lip 20 i thereby increasing the centrifugal mass onthe exterior radius of the seal and providing an easily deformablelocalized bearing surface.

In operation each compressor disc assembly 10 comprises one stage withina multistage axial compressor. Each stage progressively compresses theintake air, thus the radial dimension of the disc 15 and the size ofblades 16 are adjusted to conform with the theoretical volumetricdecrease of the gas upon compression. Accordingly, the leakage rate forthe same mass flow rate within any stage increases with the pressuredifferential across that stage since the leakage area is generallyconstant. The present invention utilizes this pressure differential APacross the compressor stage in order to provide sealing. The inventiveseal 11 is formed from a metallic foil in the order to 2 to 3 millsthick attached by diffusion bonding at the inside radius thereof to theperipheral flange 14 of disc 15. Although other methods of bonding arepossible within the scope of the present invention diffusion bondingoffers the best compromise of durability and weight. The installation ofblade locks 19 can be performed through the open side of the disc,however, in the case where blade lock insertion is necessarily from thesealed side appropriate openings, where .necessary, are provided in theseal. Blade replacement is not restricted by the seal since theinstallation can be from either side in view of the flexibility of seal1 1.

Some of the many advantages of the present invention should now bereadily apparent. The inventive seal reduces leakage across thecompressor stages of a gas turbine engine, characteristically a majorconcern in the development of gas turbines, without affecting thecritical design parameters of the compressor disc itself such as stressdistribution, changing of disc modes and disc loading. Thus the seal isadaptable to be installed on existing compressors without entailinglarge expenses in disc alteration. Above features are possible in viewof the advantageous utilization of centrifugal forces and pressuredifferentials by the invention allowing for a seal structure whichminimally affects the critical parameters of the disc.

Obviously many. modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In a multistage axial compressor having replaceable blades mounted intransverse slots around the periphery of each disc, the improvementcomprising:

annular sealing means concentrically disposed near the periphery of eachdisc on the high pressure side occluding the exposed ends of the slotsfor preventing fluid leakage therethrough, said sealing meanscompliantly mating with the disc and attached adjacent to the disc alongthe inside edge by difiusion bonding, the outer edge extending outwardlyto be urged into sealing contact across the slots when subjected to acentrifugal force and pressure difierential, said sealing means furtherbeing formed of a metallic foil in the order of 2 to 3 mills thicknessand having a deformable bead at the outer edge thereof adjacent to thedisc.

2. A rotor, comprising:

a disc including a peripheral rim with axial-facing surfaces increasingin cross section radially outwardly, and having a plurality ofconvoluted transverse slots about the rim formed to receive removableblades;

blades having root sections with axial-facing surfaces coplanar with therim surfaces inserted in each of the slots; and

a continuous annular seal concentrically attached near the inner edgethereof to the side of the disc occluding the exposed ends of the slots.

3. A rotor according to claim 2, further comprising: said annular sealbeing flexible and compliantly mating with the rim and attached adjacentto the rim along the inside edge, the outer edge extending outwardly tobe urged into sealing contact across the slots when subjected to acentrifugal force and pressure differential.

4. A rotor according to claim 3 further comprising:

said annular seal being formed of a metallic foil in the order of 2 to 3mills thickness and attached to the disc by diffusion bonding.

5. A rotor according to claim 4, further comprising:

said annular seal having a deformable bead at the outer edge thereofadjacent to the disc.

6. A rotor according to claim 5, further comprising:

a plurality of key means respectively interposed between said blades andsaid disc for retaining said blades to said disc; and

cutouts formed in said seal for permitting installation of said keys.

1. In a multistage axial compressor having replaceable blades mounted intransverse slots around the periphery of each disc, the improvementcomprising: annular sealing means concentrically disposed near theperiphery of each disc on the high pressure side occluding the exposedends of the slots for preventing fluid leakage therethrough, saidsealing means compliantly mating with the disc and attached adjacent tothe disc along the inside edge by diffusion bonding, the outer edgeextending outwardly to be urged into sealing contact across the slotswhen subjected to a centrifugal force and pressure differential, saidsealing means further being formed of a metallic foil in the order of 2to 3 mills thickness and having a deformable bead at the outer edgethereof adjacent to the disc.
 2. A rotor, comprising: a disc including aperipheral rim with axial-facing surfaces increasing in cross sectionradially outwardly, and having a plurality of convoluted transverseslots about the rim formed to receive removable blades; blades havingroot sections with axial-facing surfaces coplanar with the rim surfacesinserted in each of the slots; and a continuous annular sealconcentrically attached near the inner edge thereof to the side of thedisc occluding the exposed ends of the slots.
 3. A rotor according toclaim 2, further comprising: said annular seal being flexible andcompliantly mating with the rim and attached adjacent to the rim alongthe inside edge, the outer edge extending outwardly to be urged intosealing contact across the slots when subjected to a centrifugal forceand pressure differential.
 4. A rotor according to claim 3 furthercomprising: said annular seal being formed of a metallic foil in theorder of 2 to 3 mills thickness and attached to the disc by diffusionbonding.
 5. A rotor according to claim 4, further comprising: saidannular seal having a deformable bead at the outer edge thereof adjacentto the disc.
 6. A rotor according to claim 5, further comprising: aplurality of key means respectively interposed between said blades andsaid disc for retaining said blades to said disc; and cutouts formed insaid seal for permitting installation of said keys.